A vehicle such as an automobile comprises a power steering device which uses oil pressure. To supply this oil pressure, a vane pump is used such as is shown in FIG. 11 and FIG. 12.
This vane pump houses a cam ring 30, rotor 31 and vanes 32 which form a pump cartridge 3 inside the inner circumference of a body 107. The cam ring 30 and rotor 31 are positioned between a cover 106 fastened to the body 107 and a side plate 108 fixed to the inner circumference of the body 107.
The rotor 31 is joined to a drive shaft 100 which passes through the body 107. A pulley connected to an engine is joined to one end of the drive shaft 100. The drive shaft 100 drives the rotor 31 and vanes 32. The drive shaft 100 is supported by a bearing 120 provided on the inner circumference of the body 107 and a bearing 121 provided on the inner circumference of the cover 106. The drive shaft 100 is housed inside the cover 106, and does not pass through the cover 106.
The body 107 contains a high pressure chamber 101 formed between the inner wall of the body 107 and the side plate 108, a passage 111 connecting the high pressure chamber 101 and a valve cavity housing a flow regulating valve 4, an intake connector 105 connected to the outside of the body 107, and a low pressure passage 109 for recirculating surplus hydraulic fluid in the flow regulating valve 4 back to the pump cartridge 3. Hydraulic fluid supplied under pressure from the pump cartridge 3 via a throughhole in the side plate 108 is supplied to a power steering device, not illustrated, via the passage 111 and flow regulating valve 4. Surplus hydraulic fluid from the flow regulating valve 4 and hydraulic fluid from the intake connector 105 flow into the interior of the cover 106 from the low pressure passage 109, and are sent to intake regions of the pump cartridge 3 via branch passages 102, 102. The branch passages 102, 102 are formed in a bent shape inside the cover 106. As the cover 106 comprises the branch passages 102, 102, it is formed by demolding with a core. In a sliding region between the cover 106 and rotor 31, or between the cover 106 and vanes 32, strength is maintained by a thick part 106A having a predetermined thickness formed between the branch passages 102 and sliding surface.
On the other hand, hydraulic fluid which has leaked from one face of the cam ring 30, and from the sliding surface between the rotor 31 and side plate 108, is recirculated to the low pressure passage 109 from the outer circumference of the bearing 120 via the drain passage 112. The drain passage 112 is slanted at a predetermined angle relative to the drive shaft 100.
In addition to the vane pump described above, another example of a vane pump housing a pump cartridge inside a body is disclosed in Jikkou-Sho 61-36794. Therein, a rotor 222 joined to a shaft 224 is housed inside a body 210, as shown in FIG. 13. This rotor 222 is gripped by a pair of side plates 215, 216. The side plate 216 nearer the end of the drive shaft is housed within the inner circumference of a cover 212 joined to the body 210. A high pressure chamber 237 is formed between this side plate 216 and the cover 212. A cam ring 214 and the rotor 222 are gripped between the side plates 216, 215 by hydraulic fluid at high pressure which is led to this high pressure chamber 237.
A low pressure intake chamber 229 is formed along the outer circumference of the cam ring 214. Hydraulic fluid in the intake chamber 229 is aspirated from intake regions of the side plates 215, 216.
However according to the first prior art, in order to form the hollow branch passages 102 and thick part 106A inside the cover 106, the cover 106 has to be formed by gravity diecasting using a core (gravity mold casting). Due to the use of a core, the cover 106 cannot be manufactured by diecasting which is more productive, and it is difficult to reduce manufacturing costs and make the cover more compact and lightweight. The slanting drain passage 112 and the valve cavity housing the flow regulating valve 4 inside the body 107 are formed by machining after casting. Due to the slanting passage 112, the dimensions of the vane pump cannot be reduced in the axial direction. This leads to an increase in the number of machining steps, and higher manufacturing costs. Further, the drive shaft 100 is supported by the bearing 121 which is provided in the cover 106. The contact surface between the cover 106 and body 107 must be precision-finished in order to ensure orthogonality of the cover 106 and drive shaft 100, and concentricity of the bearing 121 and drive shaft 100. This also leads to an increase in the number of machining steps, longer machining time, and higher production cost. To house the cam ring 30 inside the inner circumference of the body 107 so that its entire circumference is enclosed, a partition 109A must be provided between the low pressure passage 109 and cam ring 30, which makes it difficult to make the vane pump more compact and lightweight in the radial direction.
Also, according to the second prior art, the number of parts increases due to the two side plates 215,216. As the side plate 216 is housed by the cover 212, the cover 212 must be formed in a hollow shape, which leads to an increase in the number of machining steps and machining time. In order to form the high pressure chamber 237 by enclosing a seal ring 238 between this cover 212 and side plate 216, it is necessary to precision-machine the contact surfaces, and to form a groove to enclose the seal ring 238. This again leads to an increase in the number of machining steps, machining time and manufacturing costs. Further, the intake chamber 229 is formed over the whole of the outer circumference of the cam ring 214, which makes the body 107 bulkier in the radial direction, and makes it difficult to make the pump more compact.
According to the vane pump of this invention, there is no hollow passage formed inside the cover, core manufacture and machining steps are omitted, and the structure of the cover is simplified. Since a core is no longer necessary to produce the vane pump, the pump can be manufactured by diecasting. This simplifies machining of the body and cover, and the vane pump can be made more compact and lightweight.